May 20, 2013 at 3:24 pm #1303160
Last week I bought some cheap and light stainless steel mugs/pots from a hole-in-the-wall store in Oakland's Chinatown (thanks Harald Hope) and this weekend I made a windscreen based on this article by Jerry Adams.
During a test boil with no wind and the stove on a low setting I could touch the top of the canister but not leave my finger there as it was too hot. The bottom/side of the canister was cold. Was this safe?May 20, 2013 at 3:31 pm #1988044
@b-g-2-2Locale: Silicon Valley
It wouldn't take much effort to put a metal heat reflector between the burner and the canister. That could be any sort of metal, even aluminum foil.
However, if you look closely in the photo, the burner appears to be a Monatauk Gnat or something similar, and it has a very short metal construction. It might be conducting heat down to the canister, and you are unlikely to fix that. I would suggest to do the reflector.
–B.G.–May 20, 2013 at 3:37 pm #1988047
Gary DunckelBPL Member
I don't thinks it's safe. It appears that the windscreen is snugly in contact with the pot, eliminating the chimney effect to let the heat escape upwards (and warming up the sides of the pot as it does). I expect that the heat hits the bottom of your pot, and some of it then exits through your exhaust holes, and some of it is deflected downward to your canister.
Have you tried this with the very lowest possible flame setting? If that works and doesn't heat the canister much, then you might have a real efficient stove, the only expense would be the longer time to boil.
I have done this sort of thing with my SP 600 pot and a titanium foil screen, but I have about 1/2" clearance between the pot and screen. I use a very low flame setting, and I am amazed at how little fuel it takes to achieve a boil.May 20, 2013 at 3:37 pm #1988048
@lunchandynnerLocale: Pacific Northwest
If it was too hot to keep your finger there, then it is unsafe.
Try cutting a circle heat reflector to place below the flames to reflect
the heat up. Like this:http://www.backcountry.com/snow-peak-gigapower-windscreen
Cut something out like that to fit your stove then put your wind screen on.May 20, 2013 at 3:37 pm #1988049
FYI, the stove is a Snowpeak Gigapower.May 20, 2013 at 3:40 pm #1988051
@b-g-2-2Locale: Silicon Valley
I think Gary hit the nail on the head.
For most butane canister stoves, the optimum spacing for the windscreen around the cook pot is about so that you can slide your pinky finger in there.
–B.G.–May 20, 2013 at 3:46 pm #1988053
> If it was too hot to keep your finger there, then it is unsafe.
Is this the rule of thumb for preventing canisters from overheating?May 20, 2013 at 4:02 pm #1988058
Yeah, one of Roger's articles said that if the canister gets warm to touch it's too warm and there's a chance it will burst.
I never noticed my canister getting warm when I did the same type of windscreen. I used Coleman F1 Ultralight and MSR Pocket Rocket, maybe there's a difference with the Gnat. Maybe there's a larger distance from flame to canister or more heat conducted through stove itself.
Maybe if you turn flame down it won't heat up canister so much.May 20, 2013 at 4:09 pm #1988060
"It appears that the windscreen is snugly in contact with the pot, eliminating the chimney effect to let the heat escape upwards (and warming up the sides of the pot as it does)."
thus my next iteration:
exhaust goes up sides of pot
I still haven't convinced everyone this is a good idea, but I've happily used it many nights of backpacking and I use a little less fuel than with previous windscreen
Don't know about canister getting warm with Gnat but it doesn't with Pocket RocketMay 21, 2013 at 2:44 pm #1988424
Buck NelsonBPL Member
Looks like a great idea to me, Jerry!May 21, 2013 at 3:49 pm #1988448
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> I could touch the top of the canister but not leave my finger there as it was too
> hot. The bottom/side of the canister was cold.
Not good. Definitely NOT good.
Your problem is that the windshield is far too close to the pot – it may even be touching it. You need a gap *right around the pot* of about 15 – 20 mm.
What is happening here is that without the gap the very hot air from the flames is being pushed back down against the canister, rather than passing up beside the pot. This is both wasteful of fuel and dangerous. No, those narrow slits are not enough. The gap should go right around the pot.
What you have here might be better described as a heat exchanger (HE) rather than a windshield. No problem with a HE by itself, as long as the bottom edge does not hang down more than a few millimetres. Do not try to mix the two.
CheersMay 21, 2013 at 8:41 pm #1988530
First picture – in addition to running stove slower, maybe cut off the bottom a little so it doesn't go down so far? My version goes just a little below the flame. My logic was to get it to fit in my pot, so maybe I lucked out and also made it so canister doesn't get hot.
Second picture – very similar to first, except there are channels rather than holes at the top for the exhaust to exit. Main thing is the exhaust goes up the side of the pot, I think. Also, some heat probably gets into the aluminum and then gets transmitted to the pot (heat exchanger). But the heat exchanger part of the design is less important. Again, bottom of the windscreen/heat exchanger (whatever you want to call it) just barely goes below the flame. The port that air goes into to mix with butane is actually below the windscreen/heat exchanger.
I've been using this on a number of trips and I now use a little less than 1/4 ounce of butane to heat pint of water, before I used a little more than 1/4 ounce. What's important is that I usually heat 16 pints per trip, so I can now reliably use a 4 ounce canister rather than a little more than half an 8 ounce canister.May 22, 2013 at 1:59 pm #1988762
I guess that I don’t get it. Sure I understand adding a windscreen/heat exchanger to increase efficiency, which makes sense. What doesn’t make sense to me is adding to this type of stove. What makes a lot more sense to me is to do this with a remote canister stove like the Kovea Spider.
Messing around with windscreens on an upright canister at home is one thing, but what about actual field conditions. I would image that a fresh canister that has been sitting in the sun at noon would be a lot more sensitive than a half spent cartridge in the early morning.
I like the concept; I would just recommend using a remote canister stove. They aren’t that expensive. My 2 cents – JonMay 22, 2013 at 2:35 pm #1988778
Remote canister stoves are heavier and more expensive. They are good in cold temperatures, and recently cheaper/lighter versions have become available. A good option.
But, I have been using those two windscreens for years, 100s of nights, I do try to camp at more sheltered locations but I have experienced lots of wind.
Many other BPL people also use upright canister with windscreen in real world conditions.
Upright canister without windscreen doesn't work so good if it's windy. Uses a lot more fuel if it doesn't blow out.May 22, 2013 at 2:37 pm #1988783
Don't you also need a windscreen on remote stove? It's lower to the ground which helps, but…May 22, 2013 at 3:11 pm #1988794
All stoves benefit from a windscreen. The difference is that you can put a "tighter" fitting windscreen/ heat exchanger that can trap more heat inside on a remote canister (basically, put a remote stove in a Caldera Cone). Lots of people have done it. With upright stoves on canisters, I worry that as people push to increase efficiency that this also will push the edge on safety. For a few dollars more, a remote canister stove gives you a lot of margin to fiddle with. My 2 cents – JonMay 22, 2013 at 3:20 pm #1988797
Dale WambaughBPL Member
@dwambaughLocale: Pacific Northwest
+1 on the remote canister stove. Much better for cold weather, more stable, and less chance of becoming recipient of the Darwin Award ;) Or just buy a Jetboil and get a real heat exchanger system.
If I were going to alter that windscreen, there is nothing to stop you from suspending the windscreen from the top of the pot, allowing all kinds of room around the outside as Roger suggested. That way it doesn't need to clamp tightly on the sides of the pot.May 22, 2013 at 4:28 pm #1988820
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> I guess that I don’t get it. Sure I understand adding a windscreen/heat exchanger to
> increase efficiency, which makes sense. What doesn’t make sense to me is adding to
> this type of stove.
Two reasons for this.
* block wind from blowing the flames away from the pot. Very high wind can prevent the pot from ever boiling because the heat is just blown sideways too much.
* Keep the very hot air near the pot for better heat transfer into the pot.
The actual heat exchanger thing is very definitely secondary.
CheersMay 22, 2013 at 5:03 pm #1988827
I understand the benefits; my point is IF your canister is getting hot, then you may have an issue. I saw an earlier post where a member modified a Snow Peak Plate to act as a shield between the burner and the canister: that is very clever. Correct me if I am wrong, but a remote stove just has a lot more inherent robustness to it if you are going after a hotter, more efficinet burn chamber. – Jon
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